The present invention relates to an improved vibratory screening machine having a tiltable screen frame and an adjustable discharge weir for discharging a liquid-solid mixture onto the screen frame in differently inclined positions thereof.
By way of background, in the oil well drilling industry, drilling mud is used in the drilling process in the well known manner. However, the drilling mud is expensive and it is therefore screened to remove foreign materials and thus reclaim the mud for reuse. In drilling an oil well, various types of soil conditions are encountered, such as sand, gravel, clay, etc. For the various soils, different inclinations of the screen frame are best to thereby to obtain maximum recovery of the drilling mud. In this respect, with certain soils, it takes longer to separate the drilling mud from the soil, which is subsequently discarded, and thus it is desirable to have an upward tilt on the screening frame to thereby permit a longer contact between the liquid-solid mixture and the screening machine. For other soils it is less difficult to separate the drilling mud from the soil and thus a downwardly inclined tilt of the screen frame is desirable. However, there are certain situations wherein clay, known as "gumbo," is encountered. In a condition of this type, it is desirable to have a maximum downwardly inclination of the screen frame so as to cause the clay, which is extremely sticky, to be discharged as rapidly as possible before it can clog the screen.
In the past a vibratory screening machine has been known which had a limited degree of adjustment of the inclination of the screen frame. In this machine, a discharge spout was located at the end of the screening frame which was pivoted, and the other end could be raised and lowered. However, since the discharge spout was fixed, the adjustment of the inclination of the screen frame was very limited because as the screen frame was adjusted in inclination, the spacing varied between the discharge spout and the end of the screen frame onto which the liquid-solid mixture discharged, and thereby adversely affected the screening process.
Furthermore, in these prior types of screening machines, since the amount which the screening bed could be inclined was limited, the "gumbo" had a very long period of contact with the screen and thus tended to clog it, which required an attendant to continuously wash the screen with a high pressure spray of water during the passage of the "gumbo." Furthermore, in certain instances the screens had to be removed from the screening frame for cleaning because of the "gumbo," thereby rendering the screening process inefficient.